Typically, in the most recent wireless communication systems, a handover of user equipment (UE) from one base station (BS) to another base station is based on the characteristics of downlink communications between the user equipment and the current base station associated with the user equipment (serving base station), as compared to the characteristics of downlink communications which could be obtained with other, neighboring base stations (target or candidate base stations). In traditional radio communication network implementations, the network was typically homogeneous, i.e., all of the base stations used in a particular network were identical, or nearly identical, in their implementation and radio characteristics. Accordingly, the characteristics of neighboring base stations did not vary significantly and investigations into aspects other than those associated with the downlink, e.g., including uplink communication characteristics, for making the handover decision led to little or no improvement in return for the increased complexities and bandwidth required for performing the uplink analysis. Consequently, including uplink characteristics in the handover decision was generally not used in network implementations due, for example, to the cost in terms of signaling overhead associated with performing such additional measurements and communicating them through the network in return for relatively slight improvement in handover decisions.
For example, in the paper entitled “On the Use of Uplink Received Signal Strength Measurements for Handover”, by Konstantinos Dimou and Anders Furuskär, IEEE 2008, pp. 2567-2571, the authors explored the potential desirability of considering uplink information in the context of handover decisions given that some base stations in homogenous networks exhibited a so-called “systematic imbalance”, i.e., the condition that the average path gain is different in the downlink and the uplink of the same radio connection for a particular user equipment to a particular base station. This condition is also sometimes referred to as “uplink-downlink imbalance”. However, this article concluded that “[t]hese findings do not motivate modification of the typically used downlink-based handover mechanisms”, i.e., by considering uplink information in the handover mechanism.
As communication networks evolved, some networks shifted from a homogeneous design to a heterogeneous design, e.g., equipment such as micro-cells and pico-cells began to appear as neighboring base station cells to the macro-cell base stations. The characteristics of the different base station types in heterogeneous networks can vary significantly and, accordingly, heterogeneous networks present sometimes significant differences in the systematic imbalances between neighboring base stations or cells. These systematic imbalances can be caused by, for example, one or more of differing transmission power levels, differing numbers of transmitter and receiver antennas, different types of receivers and/or differing losses based on differing feeders in the neighboring base stations.
Accordingly, the provision of a better handover mechanism in heterogeneous networks which takes into account differences in the various equipment types which are present in heterogeneous networks is desirable.